The present invention relates to medical techniques and can be used in heart surgery for the replacement of damaged natural aortal and mitral human heart valves. The invention can also be put to use in replacing affected tricuspid and lung artery valves.
Known in the art is a heart valve prosthesis (U.S. Pat. No. 4,276,658, 1981) comprising an annular body with a pair of ledges on a surface facing a forward flow of blood, and two flaps which are provided with bearings on the side edges of each and every flap. The bearings hingeably enter into recesses on the interior surface of the body""s ledges, which permits closing and opening the flaps by rotation. The recesses on the body of the prosthesis have a spherical bottom defined by two V-like rotation limiters, which are adapted to be operatively engaged, by lateral surfaces thereof, with the flap bearings. The interior surface of the body has two diametrically opposed flat portions.
With such a construction, arrangement of the rotation limiters of flaps directly in a hinge area, and contact of their lateral surfaces with flap bearings in open and closed positions do not practically make it possible to fully wash the lateral surfaces using both forward and reverse flows of blood. This results in the appearance of hyperemic zones, which facilitate the formation of blood clots.
The possibility of thrombosis is somewhat lowered with another construction of a heart valve prosthesis (U.S. Pat. No. 4,308,624, 1982). The valve is comprised of an annular body, a closing element of two flaps with bearings on the side edges of each flap. Each of the flaps has a respective ascending and a descending surface, oriented towards the forward and reverse flows of blood, a aide edge adapted to cooperate with the interior surface of the annular body, and an edge for joining the other flap. The bearings of flaps are arranged in the recesses on the interior surface of the body with freedom to be rotated between the closing/opening positions. The limiters of flap rotation are the internal projections of the body.
The flaps are bow-shaped in a cross-sectional area, and their descending surfaces facing, in a closed position, the reverse flow of blood are made concave. On the interior surface of the body at different levels thereof are provided two diametrically opposed flat portions. The bearings of flaps are spherical to be washed with blood in the best possible way. The recesses on the interior surface of the body have a semicircular cross-sectional area and are extended and inclined 70xc2x0 to the plane perpendicular to the central line of the prosthesis. The rotation limiters are taken out of a zone of cooperation of the flap bearings with the recesses on the body""s interior surface.
When a closing element is in an open position, because of concavity of the descending surfaces of flaps, a canal is formed therebetween for a forward flow of blood to pass therethrough, and along with this, the canal""s width in the central portion of the prosthesis is maximal and diminishes towards the interior surface of the body, wherein are provided elongated recesses for flap bearings. Hydrodynamic investigations go to show that the structure of a direct flow in-between the flaps is not uniform. If in the plane perpendicular to that of the flaps, a flow is practically laminar and fills all of the section of the valve, then in the plane parallel to the edges for joining the flaps the laminar flow is observed only in the prosthesis""s central portion while a spacious hyperemic zone is there in the area of hinges, which is increased further with said shape of implementation of the flaps. The slide of flaps, in opening and/or closing positions, along the extended recesses does not impede thrombosis because it does not remove the hyperemic zones and does not provide for washing the zones of cooperation of the flap bearings with the recesses. Besides this, the flap bearings may move in an asynchronous manner along an extended recess in closing/opening the valve, a factor that will lead to the prosthesis""s unstable work expressed in the fluctuation of values of the forward and reverse flows of blood and in the difference of mechanical forces exerting an influence on the prosthesis""s elements, which lowers reliability of its operation.
The embodiment of a rotation limiter in the form of ledges on the interior surface of the body improves the washing of the prosthesis with the blood, albeit reduces at the same time the prosthesis""s flow section orxe2x80x94to be more exactxe2x80x94lowers its hemo dynamic effectiveness.
Many of the defects could not be overcome completely in both an artificial heart valve with flat petals (Patent GB 2,055,452, 1981) and in the construction of a valve with curved flaps (U.S. Pat. No. 5,397,347, 1995).
The invention, as being claimed and as set forth in the application, enables one to diminish the possibility of thrombosis by way of improving a washing step of heart valve prosthesis elements using the blood, by enhancing the reliability and hemo-dynamic effectiveness of the valve.
The prosthesis of a heart valve comprises an annular body with two flanges, and a closing element in the form of two or three flaps, which are mounted through bearings in the recesses of the body with a faculty of rotation. If the closing element has two flaps, their axes of rotation are parallel in the vicinity of the diametric plane of the valve. In this case the interior surface of the body about the entire periphery is cylindrical with no protrusions, that is the flow section of the annular body has a form of a circle and is not varied at different levels. The body has a constant height on a greater portion of a ring circle and ledges. The number of ledges is equal to that of the flaps. The ledges are provided with flap rotation limiters on the side facing the direct flow of blood. In the preferable embodiment, the ledges are W-shaped and their interior surface from the side of the direct flow of blood is inclined to the central axis of the body.
The flaps have ascending and descending surfaces facing a direct and a reverse flow of blood, respectively, a side edge for contact with the interior surface of the body, and an edge for joining the other flap. The descending surface of the flap, oriented towards the reverse flow of blood is flat while the ascending surface of the flap oriented towards the direct flow of blood is spherically concave. The least thickness of the flaps is on the axis of symmetry at the joining edge.
The recesses for bearings have a lateral cylindrical surface and a concave bottom. The flange turned to the direct flow of blood is preferably thickened, the recesses for bearings at least partially being gone into the thickened flange.
The recesses for bearings can be made in the form of a triad of communicating blind holes. which is comprised of the central and two side holes. And in the preferable embodiment, a radius of the central hole is greater than the radii of the side holes, and the depth of the central hole is greater than that of the side holes.
In case of a closing element having three flaps, each one have two joining edges obliquely converging towards the central axis of the body and, along with this, the axes of rotation of the flaps are arranged at an angle of 60xc2x0 to form the sides of an equilateral triangle. In this case the interior surface of the body has the protrusions for the recesses for bearings to be made. This permits to fasten the flaps of the closing element to the annular body more reliable.
Preferable materials for making a heart valve prosthesis are pyrocarbon or titanium with a carbon-containing surface layer, in which a carbon content decreases gradually from the surface into the depth of the material of the body. A possibility of the latter being obtained just for artificial heart valves is described in patent RU 2109495, 1998.